window.onbeforeunload = function(){ return 'Leave page?'; }; // 禁止跳转

var target_divs = document.getElementsByClassName('ppt-image-wrap')

for (var i = 0; i < target_divs.length; i++) {
	var target_img = target_divs[i].getElementsByTagName('img')[0].src
	console.log(target_img)
}